1. Field of the Invention
The present invention relates to a working electrode assembly used for the iontophoresis (ionic permeation therapy) for permeating, into the living body, an ionic medicine useful for the living body by utilizing the electrophoresis and to an iontophoresis device.
2. Description of the Related Art
The iontophoresis for permeating, into the living body, an ionic medicine useful for the living body by utilizing the electrophoresis is also called ionic permeation therapy or ion introduction method, and has been widely known as a method of administering a medicine of a required amount into a diseased part in a pain-free state.
In the iontophoresis, so far, a medicine-containing layer impregnated with an ionic medicine is placed on the living body, a working electrode is arranged on the side opposite to the living body with the medicine-containing layer sandwiched therebetween, a counter electrode is placed on the living body separated away from the medicine-containing layer, and an electric current is flown across the working electrode and the counter electrode from a power source causing the ionic medicine to permeate into the living body.
The iontophoresis is, usually, carried out by using a working electrode assembly which incorporates a working electrode and a medicine-containing layer containing an ionic medicine accompanied, however, by such inconvenience that a solvent such as water (used for dissolving the ionic medicine) is electrolyzed on the surface of the electrode causing the pH to vary or the ionic medicine which is in contact with the electrode is decomposed. To prevent the above inconvenience, therefore, there has been proposed a technology of arranging an ion-exchange membrane between the working electrode and the medicine-containing layer (see, for example, patent documents 1 to 5 described below).
That is, a voltage applied across the working electrode and the counter electrode accelerates the electrolysis of water, whereby the pH of the medicine-containing aqueous solution varies due to H+ ions and OH− ions that are formed causing the living body to be inflamed, the medicine that has come in direct contact with the electrode to be consumed upon reacting (decomposed) on the electrode surface and, besides, often forming compounds that may adversely affect the living body. According to the technologies proposed in the above patent documents 1 to 5, therefore, an ion-exchange membrane of the type that permits the passage of ions of a polarity opposite to that of the pharmacological ions of the ionic medicine is arranged between the working electrode and the medicine-containing layer to prevent the decomposition of the medicine and to prevent the H+ ions or the OH− ions formed on the electrode from migrating to the side of the medicine-containing layer.
When the ion-exchange membrane which permits the passage of ions of a polarity opposite to that of the pharmacological ions is provided between the working electrode and the medicine-containing layer, however, the ion-exchange membrane must have an increased thickness to reliably prevent the pharmacological ions from migrating to the side of the working electrode. However, an increase in the thickness of the membrane results in an increase in the electric resistance (membrane resistance) of the ion-exchange membrane and in a decrease in the energy efficiency and in the efficiency for administering the medicine.
In the iontophoresis, further, there has been proposed a technology for arranging a pharmacological ion-permeating ion-exchange membrane between the medicine-containing layer and the living body (see, for example, patent documents 3 to 5). That is, upon providing an ion-exchange membrane of the type that permits the passage of ions of the same polarity as that of the pharmacological ions of the ionic medicine, it is attempted to prevent sodium cations, potassium cations and chloride anions from migrating to the side of the working electrode assembly from the side of the living body in order to improve the efficiency for administering the medicine.
In recent years, further, study has been vigorously forwarded concerning the iontophoresis device of the portable type for carrying out the iontophoresis at any time and on any place. The portable iontophoresis device of this type uses cells such as button cells as a power source, and it becomes important to maintain a high medicine administering efficiency when a voltage value remains constant (constant voltage).
Patent document 1: JP-T-63-502404
Patent document 2: JP-T-3-504813
Patent document 3: JP-A-4-297277
Patent document 4: JP-A-2004-188188
Patent document 5: JP-A-2004-202057